External battery packs are one of the least sexy aspects of the mobile age. They’re the equivalent of the plastic gas can in the back of your trunk: stinky, unsexy, and probably empty when you need it.

Lenmar’s Helix battery pack isn’t particularly sexy, but it doesn’t smell (despite the “Undead Power” branding, which implies putrifying flesh) and it’s unlikely to be empty when you need it: it has a massive 11,000mAh battery inside, capable in theory of charging a third- or fourth-gen iPad from 0% to full. All in a battery pack not much bigger than a deck of playing cards.

The Good

The best thing to recommend the Lenmar Helix battery pack is its capacity: this is a monster of a battery to fit into a pack this small. Measuring just 4.7 inches tall, 3.1 inches wide and 0.8 inches thick at its thickest point, the Helix is about the size of a deck of playing cards, or a very small USB hard drive.

At the core of this small device is an 11,000mAh battery. That’s an impressive amount of juice, theoretically capable of charging an iPhone eight times and a Retina iPad from 0% to full.

As befits a device with this much battery crammed into it, the Helix can charge three devices at once. There are two USB ports for charging smartphones at 1A, and one for tablets at 2.4A. This means you could easily charge two iPhones and an iPad at once.

The Helix isn’t a head-turning battery pack, which is fine: it doesn’t need to be. And it does what it says on the tin, providing a lot of juice to charge your gadgets on the go, with the battery itself being charged by a micro-USB port on the side. Adornments and bling on the Helix top out at four green power indicator LEDs that tell you how much charge is left, and flash when the Helix is recharging.

So the Lenmar Helix is very portable and stuffed to the brim with electricity. That’s about all you can ask from a battery pack, isn’t it?

The Not-So-Good

Well, no. The Lenmar Helix’s drawbacks are subtle, but they are there.

First of all, the Helix takes ages to charge. That’s to be expected: an 11,000mAh battery is going to take a long time to charge. The iPad itself needs at least eight hours to charge fully from 0% to 100%, and that’s using a 2.4A charger.

Here’s the problem, though. The Lenmar Helix charges at 1.5A, meaning it takes even longer to charge than an iPad. A way to charge the Helix at 2.4A would have been welcome, because then, it would have charged at the same rate it discharges when powering an iPad. As such, even if you have an iPad plugged into the Helix while the Helix itself is charging, Lenmar’s battery pack will run out of juice.

Then there’s the issue of battery life. Something’s a little funny about the Lenmar Helix: try as we might, we couldn’t actually charge our iPad to full using the Helix, only managing about 65%. That’s still impressive, but technically, the Helix should be able to charge an iPad to full and still have some electricity left over. We have no idea where that extra juice is going, but we’re not the only ones to have this issue: iLounge also never managed to completely charge an iPad using the Helix. This is a trait shared by other 11,000mAh battery packs, like the Enerpak Vault, but that device manages to give more of a charge to an iPad… while simultaneously costing $20 less than the Helix.

Finally, the Lenmar Helix is a pretty bare bones device. Outside of the battery pack and a micro-USB cable to charge the device, there’s nothing here: no Lightning or 30-Pin cables, not even a wall charger.

The Verdict

The Lenmar Helix is an impressive battery pack, but it doesn’t quite manage what it says on the box, it’s slow to charge, and it costs about $20 more than better performing competitors. There’s a lot of juice in this battery pack for $100, but there’s room for improvement, and some of Lenmar’s competitors are making higher performing battery packs right now for a cheaper price.

Product Name: Helix Battery Pack by LenmarThe Good: Solid construction. Has a lot of battery power. Can charge three devices at once, even a third- or fourth-gen iPad.

The Bad: Takes a long time to re-charge… even longer than an iPad. Despite a massive battery that should be up to the task, can’t charge an iPad to full. Bring your own cables.

The Verdict: A good battery pack that will save your ass when you need it, but not quite as powerful as it claims to be,

About the author:

John Brownlee is a Contributing Editor. He has also written for Wired, Playboy, Boing Boing, Popular Mechanics, VentureBeat, and Gizmodo. He lives in Boston with his wife and two parakeets. You can follow him here on Twitter.